


The Definition of Love.

by TheAlwaysKind



Category: Undertale (Video Game)
Genre: M/M, Soul Bond, Soul Sex, Swearing, kingdings
Language: English
Status: In-Progress
Published: 2020-12-30
Updated: 2021-01-21
Packaged: 2021-03-10 20:20:32
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,293
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28433061
Author URL: https://archiveofourown.org/users/TheAlwaysKind/pseuds/TheAlwaysKind
Summary: W.D. Gaster is the Royal Scientist, working for the beloved King Asgore Dreemurr. However, the skeleton monster finds himself falling in love. The King had finally started moving forward from the loss of his children and his wife leaving him, it would truly be madness to try courting the King now... Right?WARNING: WILL CONTAIN NSFW! NOT A STORY FOR MINORS!
Relationships: Asgore Dreemurr/W. D. Gaster
Comments: 2
Kudos: 10





	1. Realization.

**NSFW WARNING - This chapter will contain NSFW, if you are not comfortable with it then stop reading now!**

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Gaster let out an exhausted yawn, leaning back in his chair as he stretches out his aching bones. He had been working in the lab for the entirety of the day and it was starting to catch up to him, his body yearned for the sweet embrace of sleep. He slowly stands, his legs wobbled a little under his weight, it took a moment for him to steady himself before he was able to walk to the door. Grabbing his coat from the rack, he exits the lab and walks down the path to where the River Person sat waiting on their boat.

"Good evening, could you please take me to Snowdin?" Gaster stepped onto the boat, getting settled as the River Person nodded. The boat sped off towards Snowdin, the ride there was fairly peaceful. Once they arrived, Gaster thanks the River Person and pays them the fair. The skeleton monster walks through the sleepy town, occasionally saying a quick hello to those who greeted him. Soon he arrived at his house, he takes out the key from his coat pocket and unlocks the door.

"Ah, finally. Home at last." Another yawn escapes the scientist as he takes off his coat and shoes, sleepily making his way upstairs to his bedroom. Gaster immediately flopped onto his bed, letting out a relieved sigh. It had been an extremely long day and he wanted nothing more than a good nights sleep. With one final yawn, Gaster slips under the covers and falls asleep.

* * *

**Gaster squirmed under the might that was Asgore; the goat monster, while a gentle soul, was quite intimidating to be underneath. Asgore smiles gently, leaning down to tenderly kiss Gaster's collarbone.**

**"Is everything alright? You seem rather nervous." The King couldn't help but look at the skeleton with slight concern, he didn't wish to make him uncomfortable after all. Gaster blushed a light purple, he felt rather embarrassed that he was so nervous but it couldn't be helped since this was his first time.**

**"Yes, I'm fine. This is my first time doing this." He gently wraps his arms around Asgore's shoulders, offering him a nervous but happy smile. While he was nervous yes, he was still happy that the King allowed this to happen. He was happy that he was even courting Asgore to begin with. Asgore returned the smile, placing another tender kiss onto Gaster's forehead.**

**"I understand, do not worry, we shall take things slowly." The goat monster peppers soft kisses along the skeleton's body, making him giggle as a result. He trails his kisses all the way down to Gaster's pelvis, pressing a more firm kiss on the pubic symphysis.**

**Asgore uses his forefinger and thumb to carefully but firmly stroke the pubic symphysis; making Gaster moan, his legs twitching inward slightly. The skeleton's magic activates, making his dick manifest into being. The goat monster purrs playfully upon seeing it, leaning down to slip it into his mouth. He was easily able to take it all the way to the base; Gaster lets out a shaky gasp/moan, gripping the sheets beneath him.**

**The King bobs his head up and down, using his tongue to caress the girth. His tail wagged excitedly as he listened to Gaster's pleasured moans, it encouraged him to move faster. Gaster lightly trembled, this level of pleasure was new to him but he absolutely loved it! His thoughts were starting to become lightly hazy as he lightly grips Asgore's horns, bucking his hips against the monster's mouth. Soon Asgore pulls away and licks his lips, gently turning Gaster onto his front. The skeleton was on his knees so his pelvis was presented to Asgore, it was a tad embarrassing.**

**Asgore shuffled closer, holding his cock in one hand. "Get ready." He warned softly, letting his dick slide inside. Gaster's magic flares as the size of the King's cock stretches it out. The skeleton let out a hitched breath, a shaky moan following suit. God, he figured Asgore would be big but it felt bigger than expected! Gaster grips the sheets tightly, letting himself adjust to Asgore.**

**After a moment Asgore began to thrust his hips, each one striking against Gaster's core. The skeleton moaned and whined, his irises switching to a deep pink. The goat monster barely even begun and Gaster was absolutely drooling from bliss, it felt Heavenly! Asgore gently grasped Gaster's dick and begins to stroke it while his rhythm gained speed, striking deeper until he he hilted with each thrust. Gaster cried out in pleasure, tears pricking the edges of his eye sockets.**

**"Oooh Sire~! Fuck yes! Don't stop~!" The scientist begged, the bed was rocking and creaking wildly at this point. Asgore held Gaster close, loving every sound he drew out of Gaster. He hadn't seen Gaster like this before and wanted to see much more of it, so he heeded Gaster's pleas. Slamming roughly against his rectum and stroking his dick quickly, earning jolts and spasms of pleasure.**

**"Mnn~ Such a wonderful voice you have~ Are you getting close Gaster?" Asgore purred, he felt like he was starting to get close to a climax of his own. Gaster could only nod, his mind was far too muddled to even form propper sentences. It wasn't much longer before both monsters hit their climax, Asgore pouring his hot seed inside of Gaster. The skeleton whimpered, clinging tightly to Asgore as he shook with esctasy.**

**Asgore pulls out and lays down, gently pulling Gaster into a hug. "I love you~" He cooed softly, the duo were exhausted but satisfied from their session.**

* * *

Gaster woke with a start, sweat trailing down his temples. He sat there for a moment, in a complete daze, before he was awake enough to assess his flustered state. He had never had such a vivid dream before and it was a sex dream of all things! A warm blush flushed across his face as he thought about it more, this was the equilibrium. The proof he needed. Gaster had been vaguely aware that he had feelings for Asgore but he always brushed them aside but now he had to face the music, he was very much in love.

"☝︎□︎♎︎ ♐︎◆︎♍︎🙵♓︎■︎♑︎ ♎︎♋︎❍︎■︎ ♓︎⧫︎✏︎" Gaster cursed to himself, sliding under his quilt more as if that would help him hide from the truth. He felt so guilty about the fact he loved the King, to him it felt wrong. Especially since the King had gone through so much lately, he'd be a fool to try anything now.

"You're a fool Wingdings, a Goddamn fool. It'll never work out, you're just his friend. Calm yourself." He mutters softly, he sat up and saw that he had a boner. He sighed in annoyance, this was certainly one way to start the day.

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Hey thanks for reading! I'll add any Wingding translations here at the end! I hope you enjoyed chapter 1, I look forward to writing more.

Translation: ☝︎□︎♎︎ ♐︎◆︎♍︎🙵♓︎■︎♑︎ ♎︎♋︎❍︎■︎ ♓︎⧫︎✏︎ (God fucking damn it!)


	2. Meeting With The King.

Gaster arrived at the Dreemurr Castle, more specifically he arrived just outside of the throne room, remnants of his teleportation magic fizzling into nothing. He let out a sigh of frustration, he was supposed to have been in this meeting exactly 10 minutes ago but thanks to his... _Incident_ this morning, he had been delayed. Gaster stood there for a moment longer, trying to wrack his skull for any decent excuse but any that he thought of had been said before. Asgore was most likely going to give him quite the stern talking to once he set foot inside that room; so with a slight adjustment of his coat, he did just that.

Asgore was pacing around; usually, he was sitting on his throne, reading a book or watering the flowers that the throne was surrounded by. To see him so distressed that he was actively pacing around like this was concerning, to say the least. Gaster mentally prepared himself before gently coughing; which, in turn, immediately caught the King's attention. He turns to face Gaster and almost all at once, the worry just melts away. He walked over and embraced the scientist, making him feel a tad confused.

"Oh, thank goodness, you are okay! I was so terribly worried when you did not come, are you alright?" Asgore was talking way too fast for Gaster to understand but he felt flattered that his friend was worried. He gently pats Asgore's hands, giving him a consoling look.

"Now now Sire, you needn't get so riled up over me. I appreciate your concern but I am fine, I just got lost in my work. I didn't intend to worry you." Asgore gave the skeleton a sceptical look but didn't push for any more answers.

"I am simply relieved that you are okay, please try to call me next time will you not?" Gaster blushed softly; he had a very good reason he didn't call, after all, his hands had been far too busy. The scientist nods his head, focusing himself back to the present. Asgore wanted to know about the soul containment chambers or maybe about the CORE, to be frank, Gaster wasn't entirely sure why he had been summoned.

"Of course Sire but to the task at hand, could you tell me why you summoned me?" Asgore nods, taking a few steps back. He almost forgot that he was supposed to be focusing on their meeting.

"Right. Thank you for coming Gaster, while I do wish to discuss matters on the soul containment chambers and the CORE, there is another matter that I would like to talk about." The King pauses, letting Gaster process the new information. "You see, it is almost that time of year again. **The Moonstone Festival**. Where monsters, and their partners, get together under the light of the Moonstones and refresh their vows or rekindle their soul-bonds. As you can tell, this will be the first year I do not have Toriel by my side... I... Am unsure of what to do. I do not wish to avoid this wonderful day but I also have no-one to share it with.."

Gaster nods in understanding, he didn't have a partner so he never felt the need to take part in the festival but occasionally he'd buy some food. He knew that Asgore was the social type, being holed up during the festival would be torture for him. "I could accompany you."

There was an awkward silence as Gaster screamed mentally at himself for being so stupid, he wasn't supposed to say that _out loud!_ Asgore, on the other hand, was just simply surprised. While the festival could be attended by friends, it was also intimate and passionate. A place of love comes to blossom and renew. Thinking about attending such a place with Gaster made him feel... Asgore blinks, what _was_ this feeling? A tad bit of embarrassment maybe but there was something more, lingering underneath the surface. It felt like... Excitement? 

The silence drew on for a few minutes before Gaster broke it. "I'm sorry! I-I didn't intend to offend you Sire! I-I should go." 

Asgore immediately grabbed Gaster's arm, the hold was gentle as to not inflict harm, stopping him for going anywhere. "No. Please, do not go. I do not wish for you to go. Rather, I want you to go to the festival with me. Your offer surprised me but I am happy to accept."

The skeleton blushed more, the deep purple staining the white of his cheekbones. "O-Of course Sire." For a brief moment, it felt like he was floating on air but then he forced himself down to reality. This was just a friend thing, nothing more.

"Is everything alright Gaster? You seemed flustered." Asgore was rather concerned, he wasn't use to Gaster looking like this. Usually; the scientist wore a professional, monotone expression. A soft blush of his own crept along his cheeks as he felt his soul flutter.

"Yes. Y-Yes, everything is fine. I'll see you tomorrow." The festival was tomorrow evening, just a few more hours left before the duo would spend time at the most intimate place in the Underground. The thought was thrilling! Gaster teleports out of the room before Asgore could stop him again, causing the King to sigh.

A soft smile curls onto his lips, his soul thrumming with excitement. Just one day to go.

* * *

**-Moonstone Festival - 8 PM.-**

The town square was buzzing with life, monsters of all types were here. They laughed and ate wonderful food, the atmosphere was simply wonderful! Asgore, dawned in a simple pink sweater and sweat pants, walked alongside Gaster who wore a science tee and dark trousers. 

"It is so wonderful to see so many happy faces, I can at least take solace in the knowledge my people are happy one day a year." The old goat beamed with pride, casting a passing glance at couples who were soul-bonding or cuddling. His own soul flared with the desire to do the same, to merge with another soul and bathe in its warmth. His gaze travelled to Gaster, the skeleton had bought some Monster-Floss and was eating it happily. Part of him wanted to ask Gaster to soul-bond with him but the other half was quick to shove that idea down. He wasn't sure if Gaster wanted that kind of commitment or if he was even interested in a relationship.

"Mm." Gaster takes a moment to swallow his food. "Indeed! While I don't really take part, I enjoy the atmosphere and the food." He smiles at the King, little bits of floss still stuck to his cheekbones.

Asgore chuckled, helping to clean Gaster's face with a handkerchief. "I am glad to hear that my friend." 

"A-Asgore please, I'm not a child, you don't need to-" Gaster was cut off in the middle of his sentence by Asgore pulling him into a hug, lifting him off his feet and faceplanting into the goat's shoulder. 

"I know. I could not help myself." He gently guides Gaster's face to look upward, the star-like stones glowed warmly in the dark. "Are they not beautiful Gaster~?"

"Yes Sire, very much so." The skeleton smiles; he adored the stars and even if these weren't the real ones, they were beautiful in their own way. Asgore notices the same purple blush warming the skeleton's cheekbones and felt his own increasing, seeing his longterm friend so happy made his soul warm. In fact, it started to glow, becoming noticeable under his sweater.

"S-Sire?" Gaster gasped, the warmth of Asgore's soul could be felt through the King's clothes. Even if the soul wasn't presented, the desire to touch it was beginning to creep in.

"Yes? What is the-" Asgore looked at his chest, having seen Gaster staring at it, and immediately flushed bright red. He hadn't even noticed! Oh, he felt so embarrassed! 

"O-Oh! Golly, I.. I am terribly sorry, I had not realised." The goat put his hand over his chest, covering the glow of his soul. Gaster gently pulls the hand away, replacing it with his own. 

"You don't need to apologise. I'm glad you feel this happy!" The scientist thumbed over the area softly, keeping his gaze fixated to Asgore's soul. "It's beautiful Sire, just as beautiful as the Moonstones." 

Asgore was deeply surprised by this, his soul glowing a bit brighter than before. It was asking permission to be let out, to be physically touched by the skeleton scientist. He let out a shaky sigh, he would have done this with Toriel but she wasn't coming back and once he started collecting souls his time here would be limited. He had to take a leap now before the opportunity slipped past him. 

It didn't take much effort to call forth his soul, as it was already eager to be let out, the shimmering upside-down soul glowed a tender white. Pulsing softly with desire, the King was vulnerable and nervous but at the same time, a rush of thrill washed through his being. This was it. Now or never.

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Thanks for reading! I look forward to writing more, I hope you enjoyed it! ;)


	3. Love Under The Moonstones.

**NSFW WARNING - This chapter will contain NSFW, if you are not comfortable with it then stop reading now!**

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Silence. 

The silence had been dragging out for a few minutes now, Asgore was beginning to think that presenting his soul had been a bad idea. Gaster, on the other hand, was in shock. He hadn't expected to see Asgore's soul, it was absolutely gorgeous! However, he quickly realized that he was staring so he shakes his head to clear his thoughts. The scientist ever-so-gently cups the soul in his palms, lifting it a tad closer to his face.

"Oh Sire~ Your soul is so immaculate and perfect~" Gaster pressed his teeth against the smooth surface of the soul in a tender kiss, he could feel its warmth radiating against his face and couldn't help but feel happy. It was such a comforting sensation. Asgore shivered a little, his cheeks growing brighter as he watched Gaster kiss his soul. It was an odd feeling but at the same time, it felt nice. 

"O-Oh goodness~ I am not so sure I would go that far." The goat monster chuckles softly, the compliments made his blush grow even brighter. He might turn into a tomato if this continued, not that he really minded that much. He was simply relieved Gaster wasn't upset at him for presenting his soul to him like that. Gaster chuckles too; placing another tender, but slightly more firm, kiss upon the King's soul. 

"You're far too modest Sire. Do you mind if I do this?" The skeletal monster opens his mouth, letting his magically activated tongue slip out between his teeth. His tongue proceeding to slowly drag itself along Asgore's soul, he was pleasantly surprised to taste an ever-so faint flavour of buttercups. Asgore shivered again, a soft moan/mewl barely escaping his throat. He had forgotten how sensitive a soul was, so the rush of pleasure that washed through his body was a surprise. 

"Nnn... Not at all~ P-Please, do keep going~" Asgore stuttered out his words, his brain was trying to focus on the tingling sensations so it was a tad difficult to form a sentence correctly. The scientist practically purred, a mischievous grin coming into view. He gently rubbed the surface of the soul with his thumbs, restarting his soft licking. Asgore whined quietly, feeling his legs starting to give out. So he sat on the grass riddled dirt floor, covering his mouth to keep his voice from becoming too loud. Gaster follows suit, sitting down on his knees. The skeleton licks the soul more firmly, even nibbling on its tip. 

Asgore moans, a tent becoming visible in his pants. Gaster noticed the trapped erection and blushed deeply, he was arousing the King! He couldn't help but continue to stare, he wanted to see it. He wanted to see what it looked like; what it _felt_ like, what it _tasted_ like. The skeleton monster wanted to tug down Asgore's pants and suck him off right there and then, a soft glow of purple in his own pants reflecting his desires.

The spot they had chosen was fairly remote, only one or two other couples to be seen. So Asgore didn't hesitate to push Gaster onto his back, his knees hooking over the goat's hips. Gaster let out a started yelp, looking at Asgore with both confusion and curiosity. His purple blush spreading further across his face. The King leans down, pressing kisses upon Gaster's spine/neck and along his collarbone. His large hands gently tucking into the crevices of the skeleton's pants, tugging them slowly down his hips/thighs.

Gaster's thoughts were running a mile a minute, his soul pounding against his ribcage. Was this actually happening? What did Asgore plan to do? The thrill of having sex outside slammed into his thought process, the skeleton shakily wrapping his arms around Asgore's shoulders. The King purred, slipping Gaster's pants completely off, revealing his bare pelvis. His purple coloured magic pooled within his pelvis, flaring with the desire to be filled. Asgore was quick to remove his own pants, freeing his raging boner.

The tip of his cock aligned with Gaster's pelvis, nudging against the pool of magic. Gaster whined, wiggling his hips in need/lust. God, he wanted this so bad, he wanted to be filled to the brim by Asgore's dick and then filled with his hot cum! 

"S-Sire~! Ooh, please! Please, I w-want~ I want you to fuck me!" He begged, using this moment to quickly adjust his position.

"Then get ready~" With that, Asgore pushed in. His cock slowly stretching out Gaster's magic as it accommodated for his large size, he managed to fit the entire length inside which was honestly impressive. Gaster moaned loudly, his legs trembling lightly as he was filled. He felt so full, Asgore's cock just fit so nicely inside him~ After a moment, Asgore pulled out halfway before thrusting back in. Quickly establishing a steady rhythm. Gaster clings to Asgore, his moans were a little shaky as he got used to the rocking motions. 

Asgore continued to be gentle for a little bit longer before grabbing Gaster's thighs, flipping him onto his side whilst hoisting his right leg over his shoulder. Gaster's pelvis was being held up at an angle which was very quickly taken advantage of, Asgore slamming his hips against Gaster. The angle causing his thrusts to hit deeper, the skeleton was practically melting from the pleasure. He was moaning and whining, gasping out Asgore's name between breaths. Gaster let out a sudden gasp as he felt his good spot being struck. It was so sensitive that the waves of pleasure were much more intense, tears welling in the corners of his eye sockets.

"Yes! God fuck yes, right there!" His voice was shaking with bliss but he was past giving a damn, he wanted more! He NEEDED more! Asgore was more than happy to oblige, reangling his thrusts into that good spot. Making sure to hit it harder, loving the cry of ecstasy which followed suit.

Asgore lovingly kisses Gaster's mouth, he could feel the skeleton's climax starting to grow near. Gaster combed his fingers through Asgore's golden hair, passionately returning the kiss. His soul presented itself to Asgore, his was smaller than the King's but that was to be expected. The goat holds himself closer, his own soul pressing against Gaster's. The two souls eagerly began the process of bonding, intertwining their essences and merging into one. The duo shivered, the sensation of being so close was comforting and strange. 

It wasn't long before Gaster hit his climax, crying out in pure bliss as his body was rocked with waves of intense pleasure. Asgore felt the skeleton's magic tighten around his cock, squeezing it tightly with each wave. He continued to thrust until his own limit was reached, slamming deeply into Gaster one more time before letting his cum spill inside him. The scientist whined, shaking as the warmth slowly filled his insides. This lasted for a few minutes before their climaxes ended, both panting and out of breath.

"Oh... Ooh, my stars. That... That was incredible." Gaster spoke up after a moment, still panting but calmer now.

"Most certainly, you were amazing Gaster~" Asgore purred lovingly, kissing Gaster's cheekbone tenderly. 

"Not as amazing as you were." The skeleton blushed and smiled happily, their souls separating as the bond completes. It felt so good to feel so whole, to be so full and warm. He wished he could stay like this forever. Asgore slowly pulls out, letting the cum trickle out as he laid beside Gaster. He felt just as happy, it had been a while since he felt this way and it felt amazing!

"I would love to do that again~" Gaster added, turning his tired body to face Asgore, happily snuggling into his arms. 

"I would too!" Asgore was more than eager to agree, resting his chin on top of Gaster's skull. He absolutely loved this and was more than willing to do it again, he'd do so as many times as his new soul-mate wanted. He let out a sleepy yawn, wrapping his arms around the skeleton before dozing off into a peaceful slumber. Said skeleton following quickly after.

* * *

Gaster was the first to wake; everything ached and he felt too comfortable to move but he still let out a sleepy yawn, shuffling slightly so he could fully stretch out. His bones popped quietly, sighing in content as everything readjusted. He noticed he was curled up in Asgore's arms and still very much naked, the memories of earlier flooding back and making him blush. He couldn't believe he was soul-bonded with Asgore and they actually had sex, it felt like a wonderful dream. Part of him wanted to go again, yearning for that feeling of being full and warm but he decided to wait. They were both still tired, there was no need to rush back into it.

"Hey handsome~" The skeleton whispers, placing a 'kiss' upon Asgore's lips and playfully combing through his messy golden locks. Asgore stirs lightly, mumbling something incoherent before waking from his slumber. He locks eyes with Gaster and smiles, kissing his forehead softly.

"Hello Gaster~" The sleepy King yawns, stretching out before snuggling back into Gaster. Purring in content.

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End file.
